1. Field of the Invention
This invention relates to a gasket to be used for a high-temperature joint such as a joint in mid-course of exhaust pipes connected with an automobile engine and to a method of fabricating the gasket.
2. Description of Related Art
As shown in FIG. 5, a joint 1 is normally provided in mid-course of exhaust pipes which release high-temperature exhaust gas discharged from an automobile engine to the atmosphere via a catalytic device and a silencer, in order not to propagate engine vibration directly to the catalytic device or the silencer. The joint 1 to be heated up by the exhaust gas normally incorporates a gasket 2 for preventing leakage of the exhaust gas therefrom.
The gasket 2 thus incorporated in the high-temperature joint 1 in mid-course of the exhaust pipes has been formed conventionally in the following manners that: a heat-resistant sheet 3 made of a combustible graphite sheet (an expanded graphite sheet) and a reinforcing member 4 made of a braid-over-braid knitted stainless wire fabric are mixed and integrated together as shown in FIG. 6A; the reinforcing member 4 integrated with the heat-resistant sheet 3 are then wound into a tubular shape as shown in FIG. 6B; the tubularly wound object is pressed in a mold, whereby the tubularly wound object is formed into an annular object having a hemispheric outer peripheral face corresponding to the cuplike joint 1 as shown in FIGS. 6C and 6D; and coverture 5 made of an antifriction material such as boron nitride, mica, silica, alumina, or polytetrafluoroethylene resin is provided on the outer peripheral face of the annular object by coating for the purpose of reducing abnormal friction sounds and a coefficient of friction.
Incidentally, the above-described gasket 2 for a high-temperature joint has been conventionally used in a temperature range up to 500° C. However, as emission control is more tightened in recent years, the temperature of the exhaust gas is increased whereby the gasket is exposed to an environment at the temperature exceeding 500° C. Such a temperature rise has incurred a problem that the conventional combustible graphite sheet (the expanded graphite sheet) as the heat-resistant sheet 3 for the gasket 2 might not be durable for use because the heat-resistant sheet 3 would be sublimated and decomposed under oxidizing atmosphere above 500° C. With that in mind, the inventor of this invention has actually conducted a proof test by means of fitting the conventional gasket 2 to the joint 1 in mid-course of the exhaust pipes connected with the engine. Upon visual check of the gasket 2 after the test, it was only the stainless wire fabric of the reinforcing member 4 that was observed.